1. Field of the Invention
The present invention relates to a locking device, and more particularly to a locking device capable of securely maintaining a locking state thereof, as in a box type configuration, while eliminating a limitation on the application thereof, which is involved in the case of the box type configuration.
2. Description of the Prior Art
A locking device, which has a box type configuration, typically includes a plurality of key plates each having a key groove. The key plates are mounted in a stacked state in a housing of the locking device in such a fashion that they can be hinged by a rotation of a key while being resiliently urged by a resilient member. In accordance with the hinging of the key plates, the locking device is switched between its locking state and its lock releasing state.
In this locking device, an engagement member, which is operatively connected to the key plates, moves between its locking position and its lock releasing position by the rotation of the key. At the lock releasing position, the engagement member engages with grooves formed at the key plates, thereby causing the key plates to be held at fixed positions, respectively.
Since this locking device uses a large number of key plates, it can securely maintain its locking state. Accordingly, it is very difficult to release the locking state of the locking device using any means except for a designated key. However, there is a problem in that the key cannot be separated from the locking device at the lock releasing position because the key groove of the key is engaged with the key plates at the lock releasing position.
For this reason, the conventional box type locking device have been used only for locks of safes or similar devices.
Since the key cannot be separated from the locking device in the lock releasing state, such a box type locking device is used for a door lock installed at the gate of a building or other construction which is frequently opened.